High temperature titanium alloy

ABSTRACT

A TITANIUM BASE ALLOY COMPRISING 5.9 TO 6.75% ALUMINUM, 1.5 TO 2.5% TIN, 0.5 TO 2.0% ZIRCONIUM, 0.8 TO 2.0% MOLYBDENUM, 0.15 TO 0.6% BISMUTH, 0.07 TO 0.18% SILICON, LESS THAN 0.12% OXYGEN, LESS THAN 0.2% CARBON AND LESS THAN 0.1% NITROGEN, CHARACTERIZED BY GOOD ELEVATED TEMPERATURE CREEP STRENGTH.

United States Patent Oflice 3,756,810 HIGH TEMPERATURE TITANIUM ALLOY Warren M. Parris, Las Vegas, and Donald B. Hunter,

Henderson, Nev., assignor to Titanium Metals Corporation of America, Caldwell, NJ.

No Drawing. Filed Apr. 4, 1972, Ser. No. 241,075

Int. Cl. C22c 15/00; C22f 1/18 U.S. Cl. 75-1755 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel titanium base alloy and more particularly to a titanium base alloy having good elevated temperature properties.

Known titanium base alloys intended for elevated temperature applications include combinations of alpha-promoting elements such as aluminum, tin and zirconium which in proper amounts, confer elevated temperature strength to the alloy by solid solution efliects and/or by an ordering phenomenon. However, titanium base alloys containing only alpha-promoting elements have relatively low short time strengths at elevated temperatures and, therefore, a small amount (1 to 2%) of a beta-stabilizing element such as molybdenum is generally included in the alloy. Molybdenum strengthens the alloy without detracting appreciably from creep resistance. Additionally, silicon may be included as an alloying element in amounts up to about 0.5% to further enhance the short time strength at elevated temperatures.

While it is known to add the alpha-promoting elements to high temperature titanium base alloys, it is also known that the practical upper limits for the alpha-promoters and for silicon are relatively low and, in fact, have been reached in the known alloys. The addition of an excess of either alpha-promoting elements or silicon results in low retained ductility after creep exposure which is known as metallurgical instability and is undesirable.

Our invention is directed to a titanium base alloy with improved properties at elevated temperatures. The invention consists in adding bismuth to titanium alloys in an amount between 0.15% and 0.60% by weight to increase the short time strength and the creep strength of the alloys at temperatures up to about 1100 F. These improved properties are achieved without a significant decrease in the metallurgical stability of the alloys, and, therefore, ductility is retained after creep exposure. We have found that bismuth adds to the elevated creep characteristics of the alloy and, based test results set forth hereinafter, appears to interact synergistically with siliconand molybdenum in the alloy.

It has been determined that an alloy within the scope of our invention should have a composition within the following ranges:

3,756,810 Patented Sept. 4, 1973 Titanium Balance 1 Maximum.

Additionally, it has been determined that the aluminum, tin, zirconium and silicon should be present in ac cordance with the following relationship:

A preferred alloy having good creep resistance and good ductility after creep exposure as well as good short time strength at elevated temperatures and excellent notch tensile and notch bar impact properties has the following nominal composition:

Element: Weight percent Aluminum 6.25 Tin 2 Zirconium 1.5 Molybdenum 1 Bismuth 0.35 Silicon 0.1 Oxygen 1 0.1 Carbon 1 0.2 Nitrogen 1 0.1 Titanium Balance 1 Maximum.

Alloys within the scope of our invention have superior creep properties over the known elevated temperature titanium base alloys such as Ti-6Al-4V, Ti-8Al-1Mo-1V,

TABLE I 1 Percent Creep 1 defor- Y.S RA, Mo S1 B1 matlon, percent k.s.i percent 092 gag M1 52:3

0.91 fig as 33:3 L00 33:2 10 a2 23:3 103 51:? L10 it? w &2 0:2 at 11:3 1813 1.00 0.05 113 1.91 0.04 fig 2.02 0.04 333 1.80 0.05 &3 1.96 0.09 33 1.01 0.10 3g 2.07 0.09 1.93 0.09 fig l Allspecimens heat treated 1,950 F., 15 min., AC, plus 1,300 F. 1 hr., AC; 1 Creep exposure 1,000 F., 45 k.s.i., hrs. I NE=N0t creep exposed.

A consideration of Table I shows that as little as 0.15% TABLE III bismuth appreciably improves the creep strength at 1000 Creep data F. and that a synergistic improvement is obtained when Tune to 3 3 25 defmmtlo b1smuth 1s 1ncluded in an alloy WhlCh also includes Slll- 1,0001?" mum 1,100 1225mm con. Additionally, Table I shows that the duct1l1ty, ex- 121 89 pressed as percent RA is about 14.5% or greater for bismuth contents up to about .6%, but when excess bismuth 23g 36 is included in the alloy, the percent RA decreases to below 10 8 14.5% which indicates that excessive bismuth is detri- Z2 as mental to ductility. The table also shows that the molybdenum content of the alloy should be between 1.0% and 2; $2 2.0% to provide adequate short time strength without seriously reducing creep strength or ductility. $8 3 A number of additional heats was melted and the re- 189 125 sults of metallurgical tests on these alloys are set forth in a All specimens heat treated 1,950 F" 15 min, AC plus 1300 F" 1 hr" Table II. AC.

TABLE II Room temperature tensile and creep stability data 9 Tensile properties before and after exposure Percent Creep Creep def., Y.S. Percent Heat Al S11 Zr M0 B1 S1 exposure percent (k.s.i.)

141.0 20.0 V-4204 5.93 2.03 2.08 1.03 151.0 17.5 151.0 14.5 139.0 25.0 v-4203 0.05 2.00 1.90 1. 05 148.5 10.0 147.0 12.0 145.0 23.5 v-4198 5.80 1.03 1.94 1.02 155.5 10.0 151.0 14.5 130.5 23.0 v-4202 5.95 1. 90 1.91 1.01 148.0 140 122 .12

4. v-4343 0.21 2.00 1.00 1.02 mm 13,5 139.5 21.0 V-4300 5.90 2. 00 2.04 1.09 150.5 14.0 31-2 V-4320 0.05 2.09 1.78 1.00 148:5 1316 152.5 9.5 152.0 20.0 v-4338 5.99 2.01 2.10 1.05 103.5 13.5 159.5 10.0 153.5 19.5 V-4339 0.01 2.04 2.09 1.07 100.5 10.5 105.0 8.0 150.0 19.0 v-4342 5.94 2. 01 1.72 1. 05 159.5 12.0 159.5 9.0 134.5 28.0 V-4249 5.95 2.04 1.84 0.50 145.0 22.5 142.5 22.0 139.0 25.0 V-4321 0.33 2.13 0.28 0.50 148.5 18.0 140.0 18.5 134.0 29.5 V-4292 0.13 1.98 0.45 1.12 145.0 24.5 144.0 21.0 130. 20.5 v-4293 0.28 2.14 1.54 1.14 148.0 17.5 140.5 13.0 135.5 22.0 V-4294 0.10 2.12 2.34 1.12 143.5 17.0 149.0 10.5 137.5 27.5 v-4295 0.38 1.08 2.08 1.13 142.0 19.5 142.5 17.5 137.5 20.5 v-4290 5.00 3.14 2. 09 1.07 0.30 147.0 18.0 145.0 14.5

9 All specimens heat treated 1,950 F., 15 min., AC plus 1,300 F., 1 hr., AC. 9 1,000 1 k.s.i., 144 hrs. a 1,100 F., 25 k.s.i., 144 hrs.

Additionally, optical creep tests were performed on each heat in Table II to determine the time to reach 0.2% deformation. The results of these tests are shown in Table III.

As can be seen from both Tables II and IH, several of the heats showed excellent combinations of room temperature strength, creep strength and retained ductility after creep exposure. The alloy having the best all-around 5 6 properties for use at temperatures up to 1100 F. was The ultimate tensile strength and the yield strength of heat V-4293, which has a composition well within the this alloy for short periods at elevated temperatures are commercial range of our preferred nominal composition. excellent.

The level of interstitial impurities and particularly oxy- Notch tests were conducted on various alloys within gen must be considered in high temperature titanium base our composition range to determine the notch toughness alloys. It is necessary to determine the amount of oxygen 5 characteristics of the alloys. The results of these tests are which can be tolerated without an excessive loss of post shown in Table VI.

TABLE VI Notch Properties Notch b Notched tensile bar Heat strength impact Notch time, i180l7lJIO,- No. (k.s.i.) (ft-lbs.) Notch time fracture 6 after creep exposure V4264.-. 221.0 31 Failed 1 min. at 230 k.s.t. V4263 214.5 30 Failed 2 mins. at 200 k.s.i. V-4198 223. 25 1 Failed 25 mins., 210 lr.s.i. Failed loading at 200 k.s.i. V-4262 214.0 31 Failed 9 mins. at 210 k.s.i. V4300 214. 30 Failed 2 hrs., 200 k.s.i Failed 50 mine. at 200 k.s.i. V-4320- 217.0 Failed 3 ruins, 210 k.s.i V4249- 210.5 31 V-429EL- 215. l]

I Heat treatment: 1,950 F., 15 min., AC plus 1,300 F., 1 hr., AG.

b Notch acuity K0, 8.

0 Loaded 5 hours at 150 k.s.i.1oad increased 10 k.s.i. every 5 hours to failure. 11 Samples given 1,000 F. creep exposure, then notch machined after exposure.

creep exposure ductility. In this regard, tests have been An important factor in obtaining the optimum combiconducted on three nominal Ti-6.25Al-2Sn-1.5Zr-0.3Monation of properties for elevated temperature applications l.0Bi-0.lSi alloys having difierent amounts of oxygen. in titanium base alloys within our novel composition The results of these tests are shown in Table IV, range is the manner in which an article formed from the TABLE Iv 25 alloy is heat treated. In treating articles made from an Efleet of 01011 creep stability 11 alloy in accordance with our invention, the first step Nominal oree i UTS YS P t should be either a beta anneal or beta working. This Heat 3, 332$ 5 3 f 23 should be followed by an intermediateanneal relatively low 1n the alpha-beta phase region which, 1n turn, may

fig-g g be followed by aging. The effects of exemplary heat treatv-43s4 164:5 15810 1 ments consisting of heating the metal above its beta V4363 ii i333 14 8 t ansus temperature, annealing within the alpha-beta phase A Heat treatment: 1,050 11., 15111111.,110 lus 1,300 1 1 111., AG. f Wlth and wlthout agmg f Show for b Creep exposure: 1,000 F., 60 k.s.i., 144 hrs. a Tl-6Al-2Sn-2Zr-lMo-0.35B1-0.12S1 alloy 1n Table VII.

TABLE v11 Creep Percent Notch bar deformation, U.T.S. Y.S. impact Heat treatment percent (k.s.i.) (k.s.i.) RA Elong. u (tt.-1bs.) 1,000 F., 15 111111.,110 plus 1,700 F., 1 111., AG fig fig 32 1,000 F., 15 111111., AC plus 1,700 F., 1 111.,110 plus 1,100 r., 8 hrs., A0 212 3 1% 1,000 F., 15111111.,110 plus 1,500 F.,1hr., AC 8 5&3 1,000 1 2,111 111111.110 plus 15,-F., 1 111.,110 plus 1,100 11., 8 hrs., AC Pg; g g; 4 9 .0 1,000 F.,15111111.,Ao 111111300 F.,1hr.,AO i2 fig no 1,000 F., 15111111., AC plus 1,300 11.,1 111.,110 plus 1,100 r., 8 hrs AC 10 313 152 1,000 1 15 111111., cool at 2110 1 .1111. to 1,300 F., AG plus 1,100 1 8 hrs., AC ;:8

I Creep exposure: 1,000 F., 50 k.s.i., 144 hrs. b Not exposed. a One inch gauge length.

It is apparent from the percent RA in Table IV that an Table VII shows that the heat treatment for the best increase in oxygen from 0.1% to 0.15% causes an apcombination of creep resistance, post exposure ductility preciable decrease in post exposure ductility and that an and notch bar impact properties is a beta anneal at 1900" oxygen content of 0.2% makes the alloy brittle after creep F. followed by cooling at an intermediate rate and an exposure. Based upon this data, it has been determined anneal at 1300 E, which is low in the alpha-beta field, that the oxygen content of our alloy should not exceed followed by aging at 1100 F. for eight hours with an 0.12%. air cool.

Tests were also conducted at various temperatures to The preferred heat treatment for an article of an alloy determine the short time elevated temperature strength of according to our invention Consists in Working of an alloy within the range of our invention. The results of Healing at a temperature above the beta transus temperthese tests are shown in Table V. ature of the alloy which is approximately 1850 F., cool- TABLE V ing at an intermediate rate and annealing at a tempera- Elevated Temperature Tensile Properties 11 ture low in the alpha-beta field, i.e. from about 1300 F. [HeatV'4198] to about 1500 F. This treatment may be followed by o U.T.S. Y. S. Percent aging at a temperature within the range of about 900 F. Test tempemm BA to about 1200 F. depending upon the specific properties 157. 0 145. 0 20. 5 desired. E81? 3%? Q3 Our invention has important features which include 110.0 00.0 32.0 good creep resistance and post exposure ductility along 182:? 3,1 3 $18 with good notch bar impact and tensile properties. 102.0 82.0 40. 0 While we have shown and described preferred embodi- 33 3 $212 gig ments of our invention, it is to be understood that the n Heat treatment: 1,050 F., 15 111111., AC plus 1,300 1 1111., no. 1 ve mm y be olherwlse embodled wlthm the scope b Room temperature, of the following clalms.

We claim:

1. A titanium base alloy consisting essentially of about: 5.9 to 6.75% aluminum, 1.5 to 2.5% tin, 0.5 2.0% Zirconium, 0.8 to 2.0% molybdenum, 0.15 to 0.6% bismuth, 0.07 to 0.18% silicon, up to 0.12% oxygen, up to 0.2% carbon, up to 0.1% nitrogen, balance titanium; said alloy being characterized by good creep resistance and good post creep ductility at temperatures up to about 1100 F.

2. An alloy as set forth in claim 1 having 6.25% aluminum, 2.0% tin, 1.5% zirconium, 1.0% molybdenum, 0.35% bismuth, 0.1% silicon, less than 0.1% oxygen, balance titanium.

3. An alloy as set forth in claim 1 wherein the total of oxygen plus nitrogen plus carbon is less than 0.2%.

4. An alloy as set forth in claim 1 wherein the aluminum, tin, zirconium and silicon are present in the following relationship:

zirconium percent 6 Percent tin/3 +percent silicon 4:8

6. A process as set forth in claim 5 wherein said article is heated to a temperature above about 1850" F. and annealed at a temperature between about 1300 F. and about 1500 F.

7. A process as set forth in claim 5 including cooling said article after said anneal and aging the cooled article at a temperature between about 900 F. and about 1200 F.

8. A process as set forth in claim 7 wherein said article is aged at a temperature of about 1100 F. for about eight hours.

9. A process as set forth in claim 7 wherein said article is heated above about 1850" F., annealed at 1300 F., aged at 1100 F. for eight hours and air cooled.

References Cited UNITED STATES PATENTS 2,596,488 5/1952 Jaifee et al. 75175.5 2,669,513 2/1954 Jaffee et al. 75175.5

FOREIGN PATENTS 944,954 12/1963 Great Britain 75175.5 949,841 2/1964 Great Britain 75-175.5 1,049,210 11/1966 Great Britain 75-175.5 1,049,624 11/1966 Great Britain 75-175.5 1,124,114 8/1968 Great Britain 75-175.5 1,124,324 8/1968 Great Britain 75175.5

CHARLES N. LOVELL, Primary Examiner US. Cl. X.R. 148-133 CERTIFICATE OF "@QBRE Patent 7 56. 810 d September 4.. 1973 Invent0r(8) warren M. Parris andDonald 13. Hunter It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, Line 35, After "strength" insert and the creep strength--. Col. 1, Line 55, After "based" insert --=upon--. Table 11, C01. '3, Heat V-4292, Under the formula Al, "6. l3"

. 7 should read 6..23--.

Col. 5, Line 22, Change "0. 3 Mo" to --1. 0 Mo--. Col. 5, Line 23, Change "1.,0 Bi" to --O. 3 Bi- Claim 1, 601.. 7, Line 3, 0. 5 2a 0% zirconium" should read q- -O. 5 to 2.. 0% zirconium--. Claim 4, Col. 7, Line 19, Before "Percent tin/3" insert --Percent aluminum Signed and sealed this 19th ay of February 197M...

(SEAL) Attest:

EDWARD M.FLETCHER,JR. MARSHALL DANN Attesting Officer om r of Paten 1 F RM P uscoMM-Dc 60376-P69 ".5. GOVERNMENT PRINTING OFFICE i869 0-366-384, 

